The director of Iraq's largest hydroelectric dam shot down reports Monday that it had been seized by the radical Islamic State, saying Kurdish forces fended off an assault.

Fighters with the Islamic State, formerly the Islamic State in Iraq and Syria, or ISIS, were pushed back after gaining access to a housing compound for employees who work at the dam just north of Iraq's second largest city, Mosul, Abdul Khaliq al-Dabbagh, the director of the Mosul Dam, said.

Conflicting reports about who was in control of the dam on the Tigris River began Sunday amid news of fierce fighting between Islamic State fighters and Kurdish forces, known as Peshmerga.

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A Kurdish commander told CNN on Sunday that ISIS had taken control of it, though employees remained at the dam. But al-Dabbagh said the Peshmerga held their positions until reinforcements arrived early Monday morning.

ISIS -- known for killing dozens of people at a time and carrying out public executions, crucifixions and other acts -- has taken over large swaths of northern and western Iraq as it seeks to create an Islamic state that stretches from Syria into Iraq.

Most of the people who fled districts are minority Kurdish Yezidis, an ancient religious sect with ties to Islam, Christianity and Judaism. A large number have taken refuge in the Jabal Sinjar mountains, the United Nations said.

Kurdish fighters battled ISIS in an attempt top retake Sinjar -- a small town inhabited by the Yezidi sect -- on Monday and have been engaged in house-to-house battles in some of the fiercest fighting since the fall of Mosul to the Islamic militant group in June, a Kurdish commander said.

Both sides are using heavy weaponry, the source said. Fighting has also been reported in the border town of Rabia, with Syria-based Kurds joining the battle against Islamic State militants.

Meanwhile, the head of the Kurdistan Regional Government, Massoud Barzani, told a group of Yezidi sect leaders that his government would liberate Sinjar, according to a report on the government's website.

Barzani said the Kurds had been fighting without any help from the Iraqi government or the international community.

The State Department said Sunday that it was "actively monitoring the situation" in Sinjar and Tal Afar, and said that the United States is supporting both Iraqi security forces and Peshmerga forces in the fight against the Islamic State.

"The assault over the past 48 hours on territories along the border of the Iraqi Kurdistan Region and focusing on towns and villages populated by vulnerable minorities, demonstrates once again that this terrorist organization is a dire threat to all Iraqis, the entire region and the international community," State Department spokeswoman Jen Psaki said in a statement.